As a start you should measure the wall thickness of both barrels from chamber to muzzle. Examine the barrels for finish, pits, cuts, corrosion, and other defects. Examine the condition of the ribs. Are they firmly attached? Is there any corrosion. Do the barrel ring like a bell? Have the barrels been proofed, and if so, what is proof rating?

These question are a good start. Unless you are willing to send the gun for proof, ultimately, you must make the decision to shoot.

Phil